Phototactic behavior of Daphnia as a tool in the continuous monitoring of water quality: Experiments with a positively phototactic Daphnia magna clone

We tested the hypothesis that the use of a positively phototactic Daphnia magna clone can reduce the background noise and thereby increases the sensitivity of a continuous biomonitor that uses changes in phototactic behavior as a variable for the detection of stress caused by pollutants. We selected D. magna genotypes with a stable and predictable phototactic behavior in presence and absence of fish kairomones. Two clones were positively phototactic in absence of fish kairomones (clone C134 and C1242), and two clones (C1242 and C131) showed no significant change in behavior in response to fish kairomones. Using a simple experimental set-up, we quantified the changes in phototactic behavior of adult animals of the positive phototactic clone C134 in response to two standard pollutants, Cu2+ and pentachlorophenol (PCP). Sublethal concentrations of Cu2+ and PCP in ISO standard medium resulted in a linear decrease of the phototactic behavior of clone C134 after 3.30 h. The detection limit for changes in phototactic behavior of clone C134 was 0.045 mg l−1 for Cu2+ and 0.8 mg l−1 for PCP.